As integrated circuit packages increase in capability and complexity, the number of wires or contacts needed to interconnect the IC package to its associated substrate increases. Two of the methods used to increase the number of interconnects are to decrease the size and increase the density of wires around the sides of the IC package or form a two dimensional array of interconnects, or balls, on the underside of the IC package. Examples of these types of IC packages are the quad flat pack (QFP), which can have up to 600 wires on four sides of an IC package, or the ball grid array (BGA), which can have over 1000 solder balls that form interconnects on the bottom of the IC package. The wires or leads of a QFP and the balls of a BGA are three dimensional features. That is, the balls and wires of the various packages project away from the package.
The substrate or wafer to which the QFP or BGA attaches includes a corresponding array of pads to which the wires (“leads”) of the QFP or balls of the BGA mate. It is of critical importance in the manufacture of electronics that the individual leads or balls are coplanar with one another. If the leads or balls are not coplanar, and the IC package is soldered onto a substrate, some of the leads or balls may be in electrical contact with the substrate while others will not be. The connections between a BGA and its substrate are not subject to visual inspection. Further, once a BGA is in place it is often easier to discard the entire substrate with BGA if the BGA is faulty. That is, if a single IC package on a substrate that potentially contains numerous IC packages is not fully connected, then the entire substrate is defective and must either be repaired or discarded.
The critical nature of attaching IC packages such as QFPs or BGAs to their substrates to have connectivity has created a need to measure the coplanarity of QFPs and BGAs. In the prior art, coplanarity is often measured using a laser and a complementary metal-oxide semiconductor (CMOS) or CCD camera connected to a computer via a framegrabber. This is an extremely slow process. To facilitate increased speed of the process the prior art has proposed alternate conveyor mechanisms to convey the part in the field of view of the camera in a more expeditious manner.
The operation and application of 3-D sensors is known in the art as exemplified by U.S. Pat. Nos. 4,238,147, 4,590,367 and 5,028,799. The plane of light may be formed by a collimated laser beam spread by a cylindrical lens or by a spot of light that is deflected by a mirror mounted on a galvanometer, mechanical motion, spinning mirror, or acousto-optic deflector to form an equivalent plane made of a group of spots. The surface depth information is obtained by reading a signal for each part of the plane from a position sensor.
Despite the solutions proposed by the prior art a significant need exists to provide a higher speed product to measure coplanarity.